Project Summary The corpus callosum is a mammalian white matter structure providing the primary pathway for communication between cortical hemispheres. Deficits in callosal structure can be seen in neuropsychiatric diseases such as autism and schizophrenia and Developmental Agenesis of the Corpus Callosum is often accompanied by mental retardation and seizure (Van der Knaap et al. 2011,Paul et al., 2007). Despite this, relatively little is known about how interhemispheric processing contributes to perception and the experience dependent development of systems. Using cutting-edge in vivo imaging and neuroanatomical techniques we can begin to dissect out the role of interhemispheric processing in the context of visual perception. I aim to establish the first direct measurements of the visual response properties of interhemispheric inputs. In doing so, we have already uncovered underappreciated interhemispheric inputs from binocular visual cortex (bV1) into bV1 and higher visual area PM. Furthermore, these projections appear to be visually responsive and whereas projections to PM have similar response properties to intra-hemispheric inputs, projections onto bV1 provide high spatial frequency ipsilateral eye information not represented in the local circuit. This shows that the circuits underlying interhemispheric integration are more complex than traditional like-to-like patterning. We aim to follow up this characterization with adult DREADDs manipulation to further parse out the interhemispheric contribution on local network processing. We will also examine the hypothesis that interhemispheric silencing following monocular deprivation rescues the experience dependent plasticity. If successful, this study will provide the first direct insight into properties of interhemispheric projections and the circuits by which they affect visual perception and development. These studies will be of broader interest by providing key insight into the function of the corpus callosum.